You'll need two things:
A license key file.
A version of the license key library.
The library is a jar or dll that you add to your project. This library is used to load and validate your license key. This library will also enable the functionality in the iText 7 add-ons if there is an appropriate entry in the license key file.
To load a license key, use the following line of code:
Do note that you'll need to call this line of code before any other iText API call. Not loading the key at start up might result in the producer line having a reference to "AGPL" instead of your company name.